Response to anaplastic lymphoma kinase inhibitor in gastric cancer harboring DCTN1–ALK fusion: a case report and review

Anaplastic lymphoma kinase (<i>ALK</i>) rearrangements are exceedingly rare in gastric cancer, and uncommon fusion types add to the difficulties of proper, precise treatment strategies. Although detected in non-small cell lung cancer (NSCLC), inflammatory myofibroblastic tumors (IMTs), and Spitz tumors, the <i>DCTN1-ALK</i> fusion has not previously been reported in gastric cancer. This report describes the first case of gastric adenocarcinoma harboring a <i>DCTN1-ALK</i> fusion that was successfully treated with the ALK-targeted agent alectinib after first- and second-line chemotherapy-based regimens had failed. Progression-free survival on alectinib was 11.5 months until KRAS amplification emerged on serial circulating tumor DNA analysis, leading to rapid systemic relapse. The other documented cases with <i>DCTN1-ALK</i> fusion treated with the first or second generation of ALK inhibitors indicated this rare fusion as an actionable driver gene mutation. This successful personalized anti-tumor strategy highlights the clinical utility of comprehensive genomic profiling and liquid biopsy in detecting and monitoring actionable <i>ALK</i> fusions in solid tumors.